A problem long-standing in the art lies in the production of pneumatic tire and wheel assemblies which, when assembled and operated on a vehicle, run true about the axis of rotation. Forces generated by any circumferential variations in the tire carcass or wheel cause vibrations, which in turn lead to dissatisfied customers and significant warranty claims against automobile manufacturers. The present trend among manufacturers toward higher tire inflation pressures and smaller vehicles to improve fuel economy accentuates this problem, so that rotational uniformity of the tire and wheel assembly has become more critical than in the past.
Rotational non-uniformities in the tire and wheel assembly may possess both radial and axial components. Either or both of such components may be due to manufacturing inaccuracies in the wheel and/or in the tire mounted thereon. Axial characteristics, i.e. runout or force variations in the direction of the wheel and tire axis, are termed "lateral" characteristics in the art and in the present application.
Multipiece vehicle wheels fabricated from metal, usually steel, conventionally include a disc having a circular array of bolt openings adapted to receive mounting studs for mounting the wheel to a vehicle, and a center pilot opening adapted to be received over the wheel hub. In order to improve radial runout characteristics of the wheel, it has been and remains conventional practice in the wheel manufacturing industry to attempt to form the circle of bolt-mounting openings and the center-pilot opening coaxially with each other and with the rim tire bead seats, with the goal thus being to form a true-running wheel. A number of techniques have been proposed for accomplishing this result, including formation of the bolt and center openings with a single tool while locating off of the bead seats, machining the center opening while locating off of pre-formed bolt-mounting openings, and circumferentially permanently deforming the rim bead seats while locating off of the bolt-mounting and/or center-pilot openings.
U.S. Pat. Nos. 4,279,287 and 4,354,407, both assigned to the assignee hereof, depart from this conventional practice, and address the problem of radial runout and radial force variations in a pneumatic tire and wheel assembly by intentionally forming the bolt-mounting and/or center-pilot openings in the wheel disc at the time of wheel manufacture on an axis which is eccentrically offset from the average axis of the rim bead seats. Such radial offset is in a direction and amount which is predetermined to locate the low point or high point of the first harmonic of bead seat radial runout circumferentially adjacent to a selected location on the wheel rim, such as the rim valve hole. A pretested tire, having the location of the complementary peak of the first harmonic of radial force variation marked thereon, may then be assembled onto the wheel such that the respective tire and wheel harmonics are complementary and thereby tend to cancel each other. U.S. application Ser. No. 667,338, filed Nov. 1, 1984 by the inventor herein and assigned to the assignee hereof, discloses an improved technique for forming the bolt-mounting and center-pilot openings in either conventional or styled wheels, which technique may be employed for manufacture of either truerunning wheels with minimum radial runout or wheels of controlled eccentricity per the aforementioned patents.
It likewise has been and remains conventional practice in the wheel manufacturing industry to attempt to form true-running wheels of minimum lateral runout - i.e. wherein the mounting plane defined by the inboard surface of the wheel disc in the region of the bolt-mounting openings is parallel to the average plane of the rim bead seats. This is accomplished in accordance with the technique disclosed in Bulgrin et al U.S. Pat. No. 3,143,377, for example, by fixturing a preformed rim on a stationary annular die ring and then press-fitting a preformed disc into the rim, with the axis of press-fit being coincident with the axis of the rimfixturing ring. Problems with the technique so disclosed are that it does not directly or inferentially employ the average bead seat plane for purposes of fixturing the preformed rim, and that it does not readily accommodate adjustment for different manufacturing runs which may, and usually do, result in differing manufacturing tolerance variations in the rim and disc.